Manufacture of calcium carbid.



F. M. BECKET.

MANUFACTURE 0F CALCIUM CARBID.

APPLICATION FILED APR.|0|19I6.

Patented Jun. 21, 1919-.

5141/04/11 boa, {g1g/Jv, r.

^ UNITED STATES PATENT oEEIcE.

FREDERICK M. BECKET, OF N FALLS, NEW YORK, ASSIGNOR TO UNION CARBIDE COMPANY, OF `NEW YORK, N. Y., A CORPORATION OF VIRGINIA.

MANUFACTURE OF CALCIUM CARBID.

- Sipecication of Letters Patent.

Patented an. 21, 1919.

Applicatie@ iuednpru io, 191s. serial No. 90,207.

No. 1,137,567, patented April 27, 1915.

According to said patent, aggregates suitable for furnacing are prepared by mixing lime with a suitable coking coal, in proper proportions as therein defined, and subjecting the mixture to heat under ordinary cok.- ing conditions. According to the vpresent improvements aggregates of the desired character are prepared under special coking conditions which permitof a continuous or semi-continuous operation, whereby certain important advantages are secured, as hereinafter pointed out. As raw materials I employ a mixture of unburned limestone and a coking coal, or equivalent bituminous material, and I perform-the operations of coking the coal and burning the limestone while conveying the 'charge through a heating zone, in which, preferably, the'temperature increases toward the exit end. During the transit of the charge through the heating zone agitation or stirring of the mass is avoided. i

My. invention will be described in one spe- 40 ciiic illustrative embodiment, and in connection with apparatus as shown in the accompanying drawing, wherein the igure is a longitudinal central section. In said drawing- 1 represents a large heating chamber or tunnel-like structure of masonry, appropriately heat insulated. Within this chamber is mounted a conveying system for the charge, the essential characteristic of this system being that the mixture to be transormed into aggregates is maintained in a relatively quiescent state, that is to say, it is not subjected to material agitation or stirscribed in my prior Unitedl States Patent ring while it is being transported through the heating zone. As a diagrammatic illustration of one type of conveying systems conforming to this requirement, I have shown a continuous chain of relatively shallow cars or receptacles 2, which may be moved continuously or intermittently by any desired mechanism (not shown) in a direction preferably counter to that of the gases. These receptacles are filled successively from a storage bin 3 by means of any suitable mechanical feed device 4, and they discharge their converted contents upon conveyer 5, by which the aggregates, after crushing if required, are carried to the carbid furnaces.

G indicates a partition or apron extending from side to side of the tunnel, making a tight joint with one end thereof, and depending at its forward end into proximity to the tops of the cars 2. 7 is a burner or equivalentmeans for supplying heat at a point or points adjacent the exit end of the tunnel. If desired supplemental burners may be disposed at intervals along the walls as indicated by way of example at 8, 8. 9 is the outlet f-or the gases of combustion from the burners, commingled with carbon dioxid derived from the limestone. The volatile products from the coking operation are largely withdrawn through the-flue 10, and may be returned, preferably after beingv subjected t0 any usual treatment for the recovery of valuable by-products including ammonia, to the burners 7, 8. Fuel from other sources, as for example'coal, producer gas, oil or the like, is employed at the burners 7, 8, as may be required to supplement the heating effect of the volatile products above mentioned.

A typical operation is as follows: Limestone is crushed, for example to grains having an average diameter of about one-eighth vinch more or less, and is intimately mixed with a highly bituminous coal crushed to a like or lesser size of particle. This mixture is fed from the storage bin 3 into the receptacles 2, partly or completely filling the latter. The receptacles with their charge slowly traverse the heating zone. The time required for complete conversionl will depend upon the temperature, and also upon the depth of the bed of mixture in the cars 2.- With a depth of mixture not exceeding six inches, and a temperature at the exit end of about 1100o C., a time of transit of about three to four hours will suiiice for the production of aggregates of sufficient strength to endure the subsequent furnacing.

During the first stage of the heating the charge is moving beneath the apron 6 and is shielded from direct impingement of the flame; that is, the conditions to which the charge is subjected approximate more or less closely to those in a retort. The temperature of the charge is slowly raised and coking occurs, the bituminous constituents and volatile products from the coal passing throughth'e iue 10 to the by-product plant, if such is provided. The apron 6 may extend so far, and the rate of movement of the cars may be so controlled, that most of the bituminous matter will be expelled by the time the receptacles emerge from under the protection of the apron.

From this point the charge is subjected to the direct iniuence o'f the ame. and the burningv of the limestone to lime is accomplished, or at least' completed. I have found that this operation does not involve the destruction or material weakening of the aggregates which have been formed during the preliminary heating stages. The fully converted 'charge is dumped onto the conveyer 5, and after breaking up is carried with as little loss of heat as is practicable to the carbid furnaces.

It has been found, in operating in this manner, that for the best results rather more fixed carbon is necessary than is theoretically required by the carbid-forming reaction-- l This is in all probability due -to the fact that some oxidation of carbon takes place by reaction with the carbon dioxid present in the furnace gases, according to the equa- Accordingly, I prefer to provide about ten per cent. excess of fixed carbon in comput- .ing the charge.

with this invention may-comprise a mixture of 100 .parts by weight of unburned limestone with about 62 parts of a rich bituminous coal, represented for example by the analysisn Volatile matter 36. 48 Fixed carbon 57. 93 Ash 5. 59l

Due allowance must of course be made for the varying percentages o f ash in the coal and of lmpurities in the limestone..

v meats? As compared with the production of aggregates by a coking process carried out in a by-product oven of ordinary type, the present process offers the following advantages, among others (1) It becomes practicable to render the entire operation essentially continuous in character.

(2) The mixture to be transformed into v aggregates may be heated in relatively sha1-- low beds or masses instead of being heated in bulk throughan inclosing wall. This not only affords a more efficient utilization of the heat, but a far more rapid coking is possible. For example such shallow masses as I have referred to above may be thoroughly converted during a transit period of three to four hours, as compared with sixteen to twenty hours required for the ordinary coking operation in a by-product oven of the usual type.

(3) These relatively small masses can be broken into fragmentssuitable for furnacing with much less production of fines.

(4) The small masses are in general more uniform in character than the bulk material from a by-product oven, there being in the present case little or no tendency to the local production of fines, which tendency is common in ovens of the by-product type.

(5) The present process affords a much better control of the temperature gradient during the. colting operation, ,and this control has an important influence on the strength of the aggregates. For example, a too strong initial heating of the charge which tends always to the production of weak aggregates, is easily avoided by introducing a large proportion, or if necessary all, of the fuel at or near the exit end of the heating chamber. For the best results the charge should be heated relatively slowly at first, after which it may bebrought rapidly to full temperature.l This is very effectively accomplished in the present process by causing the charge to progress, either continuously or step by step, through a heating zone of which the temperature gradient rises toward the exit end. This effect is accentuated by the fact that the initial heating occurs practically under retorting conditions, as distinguished from heating by a direct flame. p

(6) These small masses are readily and quickly cooled below the temperature of combustion of carbon in case it is desired to store the coked material. This is especially advantageous because the character of the product is such that it cannot be fully quenched with water, as is the practice in cooling` the bulk material from an ordinary by-product coke oven.

The above enumerated advantages are possessed by the present process in common with the process disclosed and claimed in my companion application Serial No. 90,206, filed herewith, according to which the limestone is burned to lime before being mixed with the coking coal, andis thereafter coked without stirring or agitation while being conveyed through the heating zone. In addition, the present process offers the great advantage that the coking operation and the burning of the limestone take place at different points in a single structure, whereby not only are the heat losses minimized, ,but the heat of the gases from the limestone burning operation is directly availed of for the coking; while on the other hand, the gases from the coking operation, either before or after the recovery of by-products, are available for the burning of the limestone, for which purpose they may be conveyed to the burners 7, 8, as diagrammatically indicated by the broken line in the figure. This interchange of heat in a single structure may, theoretically, obviate the necessity of supplying fuel from an extraneous source; and in practice the quantity of extra fuel will be small in proportion to that required when the burning of the limestone and the coking of the lime-coal mix-ture are carried out as independent operations.

Furthermore, according to the present process the limestone may be ground, before burning, to a much finer grain than it`is practicable to employ in an ordinary limeburning operation, either in an upright kiln or in the usual smooth-walled rotary kiln; and the liberation of the carbon dioxid from these finer particles occurs more readily.

While I preferably' employ a coking coal of the type above described, or a mlxture containing a suicient proportion of such coal to assure the binding action, I may use other suitable carbonaceous materials: Thus in some cases the bituminous coal may be wholly or partly replaced by peat. The

present invention is not restricted to the use4 of any particular carbonaceous material or mixture, provided the mixture thereof with the requisite proportion of unburned limestone is capable of yielding sufficiently strong aggregates by coking.

I claim 1. In the manufacture of calcium carbid, the process of preparing aggregates suitable for furnacing, wh1ch consists in mixing with unburned limestone a carbonaceous material vserving as a source of carbon for the carbidserving as a source of carbon for ythe carbidforming reaction and furnishing also a coking binder for the mass, and coking the resulting mixture and driving off carbon di- .oxid in transit through a heating zone of informin reaction and' furnishing also a cok` ing bin er for themass, the fixed carbon of the charge being somewhat in excess ofthe requirements of the carbid-forming reaction, and coking the resulting mixture and driving off carbon dioxid in transit through a heating zone, while avoiding stirring or agitation of the mass.

4. In the manufacture of calcium carbid, the process of preparing aggregates suitable for furnacing, which consists in mixing with unburned limestone a earbonaceous material serving as a source of carbon for the carbidforming reaction and furnishing also acoking binder for the mass, the fixed carbon of the charge being somewhat in excess of the requirements of the carbid-forming reaction, and coking the resulting mixture and driving off carbon dioxid in transit through a heating zone of increasing temperature, while avoiding stirring or agitation of the mass.

5. In a process of preparing aggregates suitable for the production of calcium carbid, the step which consists in subjectin a mixture containing limestone and a suita le coking coal successively to a coking operation and a lime-burning operation while in transit through a heating zone.

6. In a process of preparing aggregates suitable for the production of calcium carbid, the step which consists in subjectin a mixture containing limestone and a suita le coking coal successively to a coking operation and a lime-burning operation, and separately withdrawing the gases from the cokin operation.

g. In a process of preparing aggregates suitable for the production of calcium carbid, the step which consists in subjectin a mixture containing limestone and a suita le coking coal successively to a coking operation and a lime-burning operation while in transit through a heating zone, and separately withdrawing the gases from the coking operation.

8. In a process of. preparing aggregates suitable for the production of calcium carbid, the steps which consist in subjectin a mixture containing limestone and a suita le coking coal successively to a coking operation and a lime-burning operation while in transit through a heating zone, and utilizing ation for the preliminary eoking of the mixture.

9. In a process of preparing aggregates suitable for the production of calcium carbid, the steps which consistlnY subjectin a mixture containing limestone and a suita le cokng coal successively to a eoking operation and alime-burning operation whlle in transit through a heating zone, utilizing the heated gases from the lune-burning operation for the preliminary eoking of the mixture, and utilizing the combustible gases from the eoking operation for burning the limestone. y

l0. In a process of preparing aggregates suitable for the production of calcium carbid, the step 'which consists in conveyiu a charge containing limestone and a suitalble coking coal through a coking zone While avoiding stirring or agitation thereof.

11. In a process ot' preparing aggregates suitable for the reduction of calcium earbid, the stepf which consists in conveyin a charge containing limestone and a suita le incase? coking coal through a coking zone of increasing temperature while avolding stirring or agitation thereof.

1Q. In a process of preparing aggregates suitable for the roduction of calcium carbid, the step whlch consists in conveyin a charge containing limestone and a suitale 'coking` coal, in the form of a relatively shalin presence of two Witnesses.

FREDERICK M. BECKE'I.

Witnesses:

SIDNEY Oris, r Meer Scare. 

